1. Field of the Invention
This invention relates to a fluid-filled vibration damping bushing suitable for use as an automotive suspension bushing or other application.
2. Description of the Related Art
In automotive suspensions to date, a vibration damping rubber is interposed between an suspension arm and a linking portion to a body side, to absorb vibration between the suspension arm and the body side. Conventionally, a tubular mounting type suspension bushing was used as a suspension bushing of this kind, so as to be able to absorb vibration while ensuring oscillation of the suspension arm. An example of a vibration damping bushing for use as a suspension bushing of this kind is depicted in FIGS. 16–18. The illustrated vibration damping bushing is of fluid-filled type having a fluid sealed within a fluid chamber.
In FIGS. 17A and 17B, a fluid-filled vibration damping bushing includes an inner tubular metal member 200 and a base rubber 202 integrally bonded by vulcanization to the outer circumferential surface of the inner tubular metal member 200. A pair of first and second fluid chambers (hereinafter simply termed fluid chambers) 204-1, 204-2 mutually independent of one another are formed in the base rubber 202, in the form of depressions recessed towards the inner tubular metal member 200 side from the outer circumferential surface thereof.
At the outer circumferential surface of the base rubber 202, an outer peripheral sleeve (here fabricated of metal) 208 having an aperture window 206 of shape corresponding to the shape of the fluid chamber 204-1, 204-2 opening on the outer circumferential surface is integrally affixed to the base rubber 202 by means of vulcanization bonding. With the fluid-filled vibration damping bushing of this example, bushing body 210 is constituted as a integrally vulcanized unit, by the aforementioned inner tubular metal member 200, base rubber 202, fluid chambers 204-1, 204-2, and outer sleeve affixed to the outer circumferential surface of the base rubber 202. A rubber wall 212 divides the fluid chambers 204-1 and 204-2.
An outer tubular metal member 214 covers openings of the fluid chambers 204-1, 204-2 from an outer circumferential side of medial plates (orifice metal members) 216-1, 216-2, and a rubber layer 218 is provided on an outer circumferential sides of the medial plates 216-1, 216-2 (these will be described later). A seal rubber layer 215 is integrally bonded by vulcanization to an inner circumferential surface of the outer tubular metal member 214 over the entire axial length, thereby giving a fluid-tight sealing to the fluid chambers 204-1, 204-2 and an orifice passage 220 (described later) by means of this seal rubber layer 215. This outer tubular metal member 214 is fastened by caulking at both axial ends thereof to the aforementioned bushing body 210.
FIG. 17A shows metal medial plates 216-1, 216-2, 216-3 embedded within the base rubber 216-4. Of these medial plates, plates 216-1, 216-2, and 216-3 form orifice metal members for the purpose of forming an orifice passage 220. A rubber layer 218 is integrally bonded by vulcanization to an outer peripheral side of each medial plate, forming at an outer circumferential surface thereof the orifice passage 220 that connects the fluid chambers 204-1, 204-2. The fluid sealed within the fluid chambers 204-1, 204-2 is able to flow from one side to the other and back again through this orifice passage 220.
The medial plates 216-1, 216-2 making up the orifice metal members are constituted as separate elements from the other medial plates 216-3, 216-4, i.e. as separate elements from the bushing body 210. At the inner circumferential surfaces of the medial plates 216-1, 216-2, stopper rubbers 222-1, 222-2 for restricting relative displacement of the inner tubular metal member 200 and the outer tubular metal member 214 in the axis-perpendicular direction, i.e. for restricting elastic deformation of the base rubber 202, are integrally bonded vulcanization projecting inward into the fluid chambers 204-1, 204-2 towards the inner tubular metal member 200.
This fluid-filled vibration damping bushing is used disposed so that the aforementioned fluid chambers 204-1 and 204-2 are situated along the principal vibration input direction. When vibration is input in the axis-perpendicular direction across the inner tubular metal member 200 and the outer tubular metal member 214 in the same direction, the base rubber 202 undergoes elastic deformation, and the liquid inside flows between the fluid chambers 204-1, 204-2 through the orifice passage 220, so that the vibration is absorbed effectively on the basis of liquid column resonance action at that time. Where elastic deformation of the base rubber 202 in the same direction attempts to go above a given level, the stopper rubbers 222-1, 222-2 come into abutment with the inner tubular metal member 200, restricting deformation above a given level.
The metal outer peripheral sleeve 208 has the following significance. Where the base rubber 202 and the outer tubular metal member 214 are affixed without interposing this kind of outer peripheral sleeve 208, the bushing body 210 including the base rubber 202 is press-fit into the interior of the outer tubular metal member 214. However, in this instance, the problem of appreciable deformation and unstable shape of the base rubber can occur, and additional problems, such as to the need to for additional process after press-metal member in order subsequently bond the base rubber 202 and the outer tubular metal member 214 (secondary vulcanization), and the need for a subsequent process to seal the liquid in the fluid chambers 204-1, 204-2, occur as well.
In contradistinction thereto, where the rigid metal outer peripheral sleeve 208 is attached to the outer circumferential surface of the base rubber 202, the base rubber 202 and the outer tubular metal member 214 can be fastened together simply by constricting the outer tubular metal member 214 in the diameter-reducing direction, and moreover this constricting operation can be carried out in liquid, so that it becomes a simple matter to seal the liquid within the fluid chambers 204-1, 204-2.
As shown in FIG. 16 and FIG. 18, these stopper rubbers 222-1, 222-2 are also constituted as separate elements from the bushing body 210, and the medial plates 216-1, 216-2 making up the orifice metal members are attached to the bushing body 210 by means of inserting them, together with the rubber layer 218 to the outer peripheral side thereof into the fluid chambers 204-1, 204-2 from the axis-perpendicular direction.
One reason for constituting the stopper rubbers 222-1, 222-2 as separate elements from the bushing body 210 and subsequently attaching them is that if the stopper rubbers 222-1, 222-2 and the base rubber 202 were constituted as a single body, the stopper rubbers 222-1, 222-2 and the base rubber 202 would inevitably have the same rubber hardness, whereas if these are constituted separately, the rubber hardness of the stopper rubbers 222-1, 222-2 can be varied freely relative to the rubber hardness of the base rubber 202, making it possible for vibration absorbing ability and stopper ability to each be better exhibited in the fluid-filled vibration damping bushing.
However, where the stopper rubbers 222-1, 222-2 are constituted separately from the base rubber 202 and designed to be attached to the base rubber 202, the fluid-filled vibration damping bushing requires a greater number of vulcanized parts (vulcanized rubber components) (here, four vulcanized parts are required), as a result of which the problem of higher cost of the fluid-filled vibration damping bushing occurs.
Additionally, as the stopper rubbers 222-1, 222-2 are situated within the fluid chambers 204-1, 204-2, during stopper action the stopper rubbers 222-1, 222-2 come into abutment with their partner components via the liquid, creating the problem of reduced frictional force and difficulty in achieving adequate stopper performance by the stopper rubbers 222-1, 222-2 (i.e. a tendency to overstroke). Additionally, there is a risk that abraded particulate material produced during stopper action of the stopper rubbers 222-1, 222-2 will be drawn into the orifice passage 220 and constrict, or in some instances clog up, the orifice passage 220.
An additional problem is that, in the event of input in the twisting direction between the inner tubular metal member 200 and the outer tubular metal member 214, i.e. input of force in a direction tilting their axes, the stopper rubbers 222-1, 222-2 can undergo appreciable strain due to abutment against the base rubber 202 in which the fluid chambers 204-1, 204-2 are formed.
While a number of problems pertaining to fluid-filled vibration damping bushings used as suspension bushings have been mentioned above, fluid-filled vibration damping bushings of this kind are used widely at various locations, with similar problems occurring in these instances as well. Fluid-filled vibration damping bushings that have a pair of stoppers for restricting displacement in the axis-perpendicular direction are taught in JP-A-8-193639 and JP-A-2003-269525, but these differ from the present invention in that the stopper pair is disposed within the fluid chambers.
JP-A-2003-269507 teaches the element of constituting a pair of annular stopper rubbers as separate elements from the base rubber and disposing these at each axial end. However, JP-A-2003-269507 does not teach a vibration damping bushing of fluid-filled, thereby being directed instead to a different purpose.